The typical marsh-type geophone has a plastic, generally tubular hollow body with a metal spike on its lower end and a cap threaded onto its upper end. The cap has a central opening through which a jacketed cable having a pair of conductor wires extends, and the wires are connected to the terminals of an acoustic wave transducer that is mounted within the hollow body. A rubber washer that surrounds the cable jacket is placed in compression as the cap is threaded onto the upper end of the body, with the aim of deforming the washer into sealing engagement between the cable jacket and the walls of the housing to prevent water from leaking into the region of the geophone terminals.
Even though the compression gland packing element may function initially to prevent water from entering along the exterior of the cable jacket, there still remains the risk that the jacket may be cut so that water can enter the jacket and migrate along the conductor wires to the interior of the housing. If the cut also extends through the insulation of a conductor wire, water can migrate along the interstices between wire strands and eventually reach the phone connections. With time, the lead wire under the rubber washer also can take a permanent set and lose the compression that is necessary to prevent leakage. Regardless of how the water gets through, the result is electrical shorting which spoils the output signals of the phone. In marsh areas, the water usually has a high salt content which quickly causes corrosion of the connections as well.
The general object of the present invention is to provide a new and improved geophone housing structure that is totally water blocked so that moisture can not enter the interior of the housing, either between housing parts or along conductor wires, so as to be particularly suitable for use in marshy areas of the earth's surface.
Another object of the present invention is to provide a new and improved method of water blocking and bonding stranded conductor wires with respect to an insulation such that moisture can not migrate along the wire strands.
Another object of the present invention is to provide a new and improved marsh-type geophone assembly that is very rugged and not subject to breakage during use or handling.